Platinum-containing MCM-41 was synthesized in a one step approach. In this new procedure, the swelling agent (toluene) was used as a transport medium to inject the Pt precursor, Pt(acetylacetonate)₂, directly into the inner core of the surfactant micelles, A 1 wt % metal loading was achieved without the loss of pore ordering, while samples with 2 wt % loading showed a less ordered structure. A total of 80-100% of the Pt precursor was incorporated in the porous host matrix depending on the precursor concentration and final loading. During the calcination process, platinum acts as a catalyst for the oxidative removal of the surfactant molecules, allowing one to decrease the calcination temperature significantly. The calcined material had a high surface area (1000-1200 m² g^-1). Platinum particles could be detected using transmission electron microscopy confirming also the absence of large particles outside the mesopore system. The in situ approach was also applied to prepare other metal/MCM-41 or oxide/MCM-41 materials such as Pd/MCM-41 and V₂O₅/MCM-41. Both of them showed a high degree of guest incorporation and no significant decrease in surface area. In situ incorporation of metals into SBA-15 resulted in a lower Pt incorporation in the final material (50-60%) and a disordered pore structure, even for low Pt loading (1wt%). The accessibility of the metallic particles for catalytic reactions was demonstrated using the hydrogenation of cinnamic acid as a model reaction. The highest specific reaction rates were observed for Pd supported on MCM-41 and were comparable to that of commercially available Pd/carbon catalysts.